1. Field of the Invention
The present invention relates to a wire with terminal including a crimp terminal mounted on an end part of an insulated wire.
2. Description of the Related Art
In the case of mounting a crimp terminal on an end part of an insulated wire, it is important that a fixing force at a crimped part is sufficiently large and connection resistance between a core and the crimp terminal is sufficiently small.
Note that the fixing force is a force required to separate the crimp terminal and the insulated wire when a force acting in a direction to pull the insulated wire from the crimp terminal is applied to a wire with terminal. Further, the connection resistance is electrical resistance between the core (conductor of the insulated wire) and the crimp terminal in the wire with terminal.
As described in Japanese Unexamined Patent Publication No. 2009-37909, a relationship of a degree of compression of a core by a core crimping portion of a crimp terminal, connection resistance and a fixing force in a wire with terminal is as described below. Note that, in the following description, a large degree of compression of the core means a small compression ratio of the core or a small crimp height of the core crimping portion. The compression ratio of the core is a ratio of a cross-sectional area of the core after compression to an initial cross-sectional area of the core. The crimp height is a height from the bottom surface to the top surface of the core crimping portion crimped to the core.
Specifically, the connection resistance is sufficiently small if the degree of compression of the core is within a predetermined proper range. However, the connection resistance increases to such an extent unsuitable for use if the degree of compression of the core falls below or exceeds that proper range.
Further, in the case that the degree of compression of the core is within a range capable of suppressing the connection resistance to a sufficiently low level, the fixing force increases as the degree of compression of the core becomes smaller. Further, in the actual wire with terminal, the degree of compression of the core varies and a correlation of the degree of compression of the core, the connection resistance and the fixing force also varies.
Accordingly, in a conventional general manufacturing process of a wire with terminal, it is necessary to strictly manage parameters of a crimping step relating to the suppression of the variation of a degree of compression of a core to reliably satisfy specifications required for connection resistance and a fixing force.
Particularly, in the case of adopting a so-called aluminum wire, a range of a degree of compression of a core to combine connection resistance and a fixing force becomes narrower and it is more difficult to combine the connection resistance and the fixing force. Note that the aluminum wire is an insulated wire including a core mainly containing aluminum and an insulation coating.
Further, in the wire with terminal shown in Japanese Unexamined Patent Publication No. 2009-37909, a part of the core crimping portion on a tip side (contact portion side) is more strongly crimped to have a higher degree of compression of the core than a part on a base end side (coating crimping portion side).
More specifically, on a bottom plate portion of the core crimping portion shown in Japanese Unexamined Patent Publication No. 2009-37909, a widthwise central part is formed without any step in a longitudinal direction of the wire. Further, parts of the bottom plate portion at opposite sides of the central part are recessed deeper in partial areas on the tip side than in the remaining areas on the base end side. Thus, steps as boundaries between the areas on the tip side and the areas on the base end side are formed at the opposite sides of the central part on the bottom plate portion of the core crimping portion.
The bottom plate portion and a pair of caulking portions of the core crimping portion are pressed by an anvil (upper die) and a crimper (lower die) of a crimping machine when the core crimping portion is crimped to the core. Note that, in the core crimping portion, the bottom plate portion is a part for supporting the core and the pair of caulking portions are parts to be folded toward the core.
If the wire with terminal shown in Japanese Unexamined Patent Publication No. 2009-37909 is adopted, it is possible to crimp parts of the core crimping portion from the steps to the tip side with strength mainly suitable to reduce the connection resistance and crimp parts from the steps to the base end side with strength mainly suitable to increase the fixing force. As a result, the parameters of the crimping step in the manufacturing of the wire with terminal are easily managed.
Note that it is also important in the manufacturing of the wire with terminal that a crimped state of the crimp terminal to the insulated wire is easily detected and the crimper and the anvil constituting a die of the crimping machine are easily manufactured.
In the wire with terminal shown in Japanese Unexamined Patent Publication No. 2009-37909, it may become necessary to form larger steps on the core crimping portion to combine the connection resistance and the fixing force. For example, in the case of adopting a thick core or in the case of adopting a core made of easily fractured metal (brittle) such as an aluminum core, the steps of the core crimping portion need to be made larger.
However, it causes cracks in the core crimping portion to form large steps on the core crimping portion in the crimping step of the core crimping portion, i.e. in the pressing step.
The present invention aims to provide a wire with terminal in which small connection resistance and a large fixing force are easily combined and a core crimping portion is unlikely to be cracked in a crimping step of the core crimping portion.